1. Field of the Invention
The present invention relates to a heat exchanger, for heating, provided with an electric heating unit structure in which heat is generated when the electric heating unit is electrically energized. The present invention also relates to an air conditioner for vehicle use into which the heat exchanger for heating is incorporated.
2. Description of the Related Art
Concerning the air conditioner for vehicle use, it is well known that an immediate heating effect can be exhibited when an electric heater is incorporated into the heat exchanger for heating.
The constitution of this prior art is described as follows. A heat exchange core portion of the heat exchanger for heating is composed of flat tubes, in which hot water (engine coolant) flows, and corrugated fins, wherein the flat tubes and the corrugated fins are laminated on each other. In a portion of this heat exchange core portion, flat tubes, to which an electric heater is attached, are provided. To be more specific, instead of the flat tubes in which hot water flows, flat tubes, to which an electric heater is attached, are provided, and the electric heater is attached to these flat tubes.
When the temperature of hot water (engine coolant) is low immediately after the vehicle engine has been started, the electric heater is energized, and heat generated by the electric heater is emitted into the air passing through the heat exchange core portion so that an immediate heating effect can be exhibited.
In this connection, the flat tubes and the corrugated fins composing the heat exchange core portion of the heat exchanger for heating are made of metal such as aluminum, the heat conductivity of which is high. Therefore, heat generated by the electric heater is conducted from the electric heater to the adjoining flat tubes, in which hot water flows, via the corrugated fins. Further, the heat is conducted to the water at low temperature flowing in the flat tubes.
As a result, it is impossible to effectively transmit the heat, which has been generated by the electric heater, to the air. Therefore, even when electric power is consumed by the electric heater, the efficiency of the immediate heating effect is deteriorated.
According to the aforementioned prior art, the electric heater is electrically energized via the heat exchange core portion by utilizing the heat exchange core portion, made of aluminum, as a conductor. Therefore, electrolytic corrosion occurs in the flat tubes and the corrugated fins.
When the heat exchanger is put into practical use, in order to ensure corrosion resistance of the heat exchanger, it is indispensable that the electric heater is attached to the heat exchanger core portion but is electrically insulated from the core portion. Therefore, the structure of the heat exchanger becomes complicated, which causes an increase in the manufacturing cost.